Apparatus and method for uplink synchronizing in multiple component carrier system

ABSTRACT

A user equipment (UE) of re-organizing a timing advance group (TAG) is provided. The UE includes: a receiving unit for receiving, from a serving base station, secondary serving cell (SCell) configuration information which includes a first field and a second field, the first field including an ScellIndex of an SCell to indicate a removal of the SCell, the second field including at least one of the ScellIndex to indicate an addition of the SCell and a TAG ID indicating a TAG of the SCell, and a radio resource control (RRC) processing unit for performing the addition of the SCell after performing the removal of the SCell from one or more SCells configured in the UE, and for reorganizing the TAG by including the SCell in the TAG.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/338,993, filed on Oct. 31, 2016, now issued as U.S. Pat. No.9,769,776, which is a continuation of U.S. patent application Ser. No.14/626,047, filed on Feb. 19, 2015, now issued as U.S. Pat. No.9,516,614, which is a continuation of U.S. patent application Ser. No.13/849,296, filed on Mar. 22, 2013, now issued as U.S. Pat. No.8,964,645, and claims priority from and the benefit of Korean PatentApplication No. 10-2012-0030216, filed on Mar. 23, 2012, all of whichare incorporated by reference for all purposes as if set forth herein.

BACKGROUND Field

The present invention relates to wireless communication and, moreparticularly, to an apparatus and method for uplink synchronization in amultiple component carrier system.

Discussion of the Background

In a common wireless communication system, although an uplink bandwidthand a downlink bandwidth are differently set, only one carrier ischiefly taken into consideration. In 3^(rd) Generation PartnershipProject (3GPP) Long Term Evolution (LTE), the number of carriers forminguplink and downlink is one based on a single carrier and the bandwidthof uplink and the bandwidth of downlink are symmetrical to each other.In this single carrier system, random access is performed using onecarrier. As multiple component carrier systems are recently introduced,random access has been able to be implemented through several componentcarriers.

A multiple component carrier system means a wireless communicationsystem capable of a carrier aggregation. The carrier aggregation istechnology in which small fragmented bands are efficiently used, and thecarrier aggregation creates an effect that uses a logically wide band byaggregating a plurality of physically continuous or discontiguous bandsin a frequency domain.

A terminal performs a random access procedure in order to access anetwork. The random access procedure can be divided into acontention-based random access procedure and a non-contention-basedrandom access procedure. The greatest difference between thecontention-based random access procedure and the non-contention-basedrandom access procedure lies in whether a random access preamble isdedicated to one terminal or not. An object of a terminal to perform arandom access procedure on a network can include initial access, ahandover, a scheduling request, and timing alignment.

In a multiple component carrier, in order to effectively perform timingalignment, a concept of a Timing Advance Group (TAG) is used. The TAG isa group of one or more serving cells having the same timing advancevalue and is configured in response to higher layer signaling. A basestation can indicate that a secondary serving cell is included in whatTAG for each secondary serving cell. For example, a base station caninform a terminal that a first secondary serving cell is included in afirst TAG, a second secondary serving cell is included in a second TAG,and a third secondary serving cell is included in a first TAG, regardingthe three secondary serving cells configured in the terminal.

However, a signaling protocol for informing that a secondary servingcell is included in what TAG has not yet been clearly defined.Furthermore, when a TAG to which a secondary serving cell belongs ischanged according to a channel condition, whether a terminal will beinformed using what method and how the method will be implemented havenot yet been disclosed.

SUMMARY

An object of the present invention is to provide an apparatus and methodfor uplink synchronization in a multiple component carrier system.

Another object of the present invention is to provide an apparatus andmethod for reorganizing a TAG based on an RRC connection reconfigurationprocedure.

Yet another object of the present invention is to provide an apparatusand method for reorganizing a TAG based on a random access procedure.

Yet further another object of the present invention is to provide anapparatus and method for sending TAG configuration information forreorganizing a TAG and secondary serving cell configuration information.

In accordance with an aspect of the present invention, there is providedUE for obtaining uplink synchronization in a multiple component carriersystem. The UE includes a random access processing unit configured tocontrol the transmission of a random access preamble used to obtain atiming advance value for the uplink timing synchronization of asecondary serving cell, a transmission unit configured to send therandom access preamble to an eNB, a reception unit configured to receivesecondary serving cell configuration information ordering the secondaryserving cell to be additionally configured in the UE, from the eNB, anda Radio Resource Control (RRC) processing unit configured to reorganizea TAG that is a set of serving cells having the same timing advancevalue so that the secondary serving cell is included in the TAG.

In accordance with another aspect of the present invention, there isprovided a method of UE obtaining uplink synchronization in a multiplecomponent carrier system. The method includes sending a random accesspreamble used to obtain a timing advance value for the uplink timingsynchronization of a secondary serving cell to an eNB, receivingsecondary serving cell configuration information, ordering the secondaryserving cell to be additionally configured in the UE, from the eNB,receiving a Random Access Response (RAR) message including a timingadvance value from the eNB as a response to the random access preamble,and reorganizing a TAG that is a set of serving cells having the sametiming advance value so that the secondary serving cell is included inthe TAG.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate exemplary embodiments of theinvention, and together with the description serve to explain theprinciples of the invention.

FIG. 1 shows a wireless communication system to which the presentinvention is applied;

FIG. 2 is a flowchart illustrating a procedure of obtaining a multipletiming advance value in accordance with an example of the presentinvention;

FIG. 3 shows a process of sending secondary serving cell configurationinformation and TAG configuration information through one RRC connectionreconfiguration procedure;

FIG. 4 is a flowchart illustrating a method of performing random accessin accordance with an example of the present invention;

FIG. 5 is a flowchart illustrating a method of reorganizing a TAG inaccordance with an example of the present invention;

FIG. 6 is a flowchart illustrating a method of reorganizing a TAG inaccordance with another example of the present invention;

FIG. 7 is a flowchart illustrating a method of reorganizing a TAG inaccordance with yet another example of the present invention;

FIG. 8 is a flowchart illustrating a method of reorganizing a TAG inaccordance with still yet another example of the present invention;

FIG. 9 is a flowchart illustrating a method of reorganizing a TAG inaccordance with further yet another example of the present invention;

FIG. 10 is a flowchart illustrating a method of reorganizing a TAG inaccordance with further yet another example of the present invention;

FIG. 11 is a flowchart illustrating a method of reorganizing a TAG inaccordance with further yet another example of the present invention;

FIG. 12 is a flowchart illustrating a method of reorganizing a TAG inaccordance with further yet another example of the present invention;

FIG. 13 is a flowchart illustrating a method of reorganizing a TAG inaccordance with further yet another example of the present invention;

FIG. 14 is a flowchart illustrating a method of UE reorganizing a TAG inaccordance with an example of the present invention;

FIG. 15 is a flowchart illustrating a method of a BS reorganizing a TAGin accordance with an example of the present invention; and

FIG. 16 is a block diagram showing UE and a BS for sending signalsregarding uplink synchronization in accordance with an example of thepresent invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Hereinafter, in this specification, the contents of the presentinvention will be described in detail in connection with some exemplaryembodiments, with reference to the accompanying drawings. It is to benoted that in assigning reference numerals to elements in the drawings,the same reference numerals denote the same elements throughout thedrawings even in cases where the elements are shown in differentdrawings. Furthermore, in describing the embodiments of the presentinvention, a detailed description of the known functions andconstitutions will be omitted if it is deemed to make the gist of thepresent invention unnecessarily vague.

Furthermore, in this specification, a wireless communication network isdescribed as the subject, but tasks performed in the wirelesscommunication network can be performed in a process in which a system(e.g., a base station) managing the wireless communication networkcontrols the wireless communication network and sends data or can beperformed by a terminal that accesses the wireless communicationnetwork. In accordance with the present invention, the wirelesscommunication system includes a communication system supporting one ormore component carriers.

FIG. 1 shows a wireless communication system to which the presentinvention is applied.

Referring to FIG. 1, a plurality of the wireless communication systems10 are widely deployed in order to provide a variety of communicationservices, such as voice and packet data. The wireless communicationsystem 10 includes one or more Base Stations (BS) 11. The BSs 11 providecommunication services to specific cells 15 a, 15 b, and 15 c. Each ofthe cells may be classified into a plurality of areas (called sectors).

User Equipment (UE) 12 may be fixed or mobile and may also be calledanother terminology, such as a Mobile Station (MS), a Mobile Terminal(MT), a User Terminal (UT), a Subscriber Station (SS), a wirelessdevice, a Personal Digital Assistant (PDA), a wireless modem, or ahandheld device. The BS 11 may also be called another terminology, suchas an evolved-NodeB (eNB), a Base Transceiver System (BTS), an accesspoint, a femto BS, a home NodeB, or a relay. The cell should beinterpreted as a comprehensive meaning that indicates some area coveredby the BS 11. The cell has a meaning that covers a variety of coverageareas, such as a mega cell, a macro cell, a micro cell, a pico cell, anda femto cell.

Hereinafter, downlink refers to communication from the BS 11 to the UE12, and uplink refers to communication from the UE 12 to the BS 11. Indownlink, a transmitter may be part of the BS 11, and a receiver may bepart of the UE 12. In uplink, a transmitter may be part of the UE 12,and a receiver may be part of the BS 11. Multiple access schemes appliedto the wireless communication system are not limited. A variety ofmultiple access schemes, such as Code Division Multiple Access (CDMA),Time Division Multiple Access (TDMA), Frequency Division Multiple Access(FDMA), Orthogonal Frequency Division Multiple Access (OFDMA), SingleCarrier-Frequency Division Multiple Access (SC-FDMA), OFDM-FDMA,OFDM-TDMA, and OFDM-CDMA, may be used. Uplink transmission and downlinktransmission may be performed in accordance with a Time Division Duplex(TDD) scheme using different times or a Frequency Division Duplex (FDD)scheme using different frequencies.

A Carrier Aggregation (CA) supports a plurality of component carriers.The CA is also called a spectrum aggregation or a bandwidth aggregation.The CA is technology in which small fragmented bands are efficientlyused. The CA can create an effect that uses a logically wide band byaggregating a plurality of physically continuous or discontiguous bandsin a frequency domain. Each of carriers aggregated by a CA is called aComponent Carrier (CC). Each of the CCs is defined by a bandwidth and acenter frequency. A CA is introduced in order to support an increasedthroughput, prevent an increase of costs due to the introduction ofwideband Radio Frequency (RF) devices, and guarantee compatibility withthe existing systems. For example, if 5 CCs are allocated as thegranularity of a carrier unit having a 20 MHz bandwidth, a maximum of a100 MHz bandwidth can be supported.

CCs may have different sizes (i.e., bandwidths). For example, assumingthat 5 CCs are used to form a 70 MHz band, a resulting configuration maybe, for example, 5 MHz CC (carrier #0)+20 MHz CC (carrier #1)+20 MHz CC(carrier #2)+20 MHz CC (carrier #3)+5 MHz CC (carrier #4).

Hereinafter, a multiple component carrier system to which the presentinvention is applied refers to a system configured to include pieces ofUE and eNBs and support a CA. In a multiple component carrier system, acontiguous CA and/or a discontiguous CA may be used and a symmetricaggregation or an asymmetric aggregation may be used. UE supporting awireless communication system according to the present invention cansupport one or more carriers, that is, a CA, depending on itscapabilities.

Hereinafter, a set of serving cells configured in one MS can be formedof only one primary serving cell or of one primary serving cell and oneor more secondary serving cells. A primary serving cell means oneserving cell which provides security inputs and NAS mobility informationin an RRC establishment or re-establishment state. At least one cell canbe configured to form a set of serving cells together with a primaryserving cell depending on the capabilities of UE. The at least one cellis called a secondary serving cell.

Meanwhile, the CC can be divided into a Primary CC (PCC) and a SecondaryCC (SCC). UE may use only one PCC or may use one or more SCCs togetherwith a PCC. UE can receive a PCC and/or one or more SCCs allocated by aneNB.

A DL CC corresponding to a primary serving cell is called a downlink PCC(DL PCC), and an UL CC corresponding to a primary serving cell is calledan uplink PCC (UL PCC). Furthermore, in downlink, a CC corresponding toa secondary serving cell is called a downlink SCC (DL SCC). In uplink, aCC corresponding to a secondary serving cell is called an uplink SCC (ULSCC). Only a DL CC may correspond to one serving cell, and both a DL CCand an UL CC may correspond to one serving cell.

Accordingly, communication between UE and an eNB performed through a DLCC or an UL CC in a carrier system has the same concept as communicationbetween UE and an eNB performed through a serving cell.

A random access procedure can be performed in order to obtain uplinksynchronization. During the random access procedure, UE obtains uplinksynchronization based on a timing advance value transmitted by an eNB.The timing advance value is indicated by a Timing Advance Command (TAC)transmitted from the eNB to the UE. The timing advance value may also becalled a timing alignment value. A random access preamble is used toobtain a timing advance value for the uplink timing synchronization of asecondary serving cell.

When uplink synchronization is obtained, UE starts a timing alignmenttimer. When the timing alignment timer operates, the UE determines thatuplink synchronization has been achieved between the UE and an eNB. Ifthe timing alignment timer expires or does not operate, the UEdetermines that uplink synchronization between the UE and the eNB hasnot been achieved and does not perform uplink transmission other thanthe transmission of a random access preamble.

Meanwhile, in a multiple component carrier system, one MS performscommunication with an eNB through a plurality of CCs or a plurality ofserving cells. If signals transmitted from UE to an eNB through aplurality of serving cells have the same time delay, the UE can obtainuplink synchronization for all the serving cells by using one timingadvance value. In contrast, if the signals transmitted from the UE tothe eNB through the plurality of serving cells have different timedelays, different timing advance values are necessary for the respectiveserving cells. That is, multiple timing alignment values are necessaryfor the plurality of serving cells. If the UE performs random accessprocedures on the respective serving cells in order to obtain themultiple timing advance values, overhead is generated in limited uplinkand downlink resources and the complexity of a synchronization trackingprocedure for maintaining uplink synchronization can be increasedbecause the number of random access procedures necessary to obtainuplink synchronization is increased. In order to reduce this overheadand complexity, a TAG is defined. A TAG may also be called a timingalignment group.

A TAG is a group including a serving cell(s) using the same timingadvance value and the same timing reference or a timing reference cellhaving the same timing reference, from among serving cells for whichuplink has been configured. For example, if a first serving cell and asecond serving cell belong to a TAG1 and the second serving cell is atiming reference cell, the same timing advance value TA1 is applied tothe first serving cell and the second serving cell, and the TA1 value isapplied to the first serving cell on the basis of the downlinksynchronization timing of the DL CC of the second serving cell. Incontrast, if the first serving cell and the second serving cell belongto respective TAG1 and TAG2, the first serving cell and the secondserving cell become timing reference cells within the respective TAG1and TAG2, and different timing advance values TA1 and TA2 are applied tothe first serving cell and the second serving cell. A TAG can include aprimary serving cell, may include at least one secondary serving cell,and may include a primary serving cell and at least one secondaryserving cell.

Each TAG includes at least one serving cell in which an UL CC has beenconfigured, and information about a serving cell mapped to each TAG iscalled TAG configuration information. A TAG is transmitted to UE throughRRC signaling when the first group configuration and groupreorganization are determined by a serving eNB which has configured acorresponding serving cell.

A primary serving cell does not change a TAG. Furthermore, UE has to beable to support two or more TAGs if multiple timing advance values arenecessary. For example, UE has to be able to support TAGs including aprimary TAG (pTAG) including a primary serving cell and a secondary TAG(sTAG) not including a primary serving cell. Here, only one pTAG isalways present, and one or more sTAGs may be present if multiple timingadvance values are necessary. A maximum number of TAGs can be set to 2or 4. Furthermore, a pTAG may always have a value of TAG ID=0 or have novalue.

FIG. 2 is a flowchart illustrating a procedure of obtaining a multipletiming advance value in accordance with an example of the presentinvention.

Referring to FIG. 2, UE and an eNB perform an RRC connectionestablishment procedure on the eNB through a selected cell at step S500.The selected cell becomes a primary serving cell. The RRC connectionestablishment procedure includes a process in which the eNB sends an RRCconnection establishment message to the UE and the UE sends an RRCconnection establishment-complete message to the eNB.

The eNB performs an RRC connection reconfiguration procedure foradditionally configuring at least one secondary serving cell in the UEat step S505. The addition of the secondary serving cell may beperformed, for example, at the request of the UE or a network or whenthe eNB determines to allocate more radio resources to the UE. Theaddition of the secondary serving cell to the UE or the release of thesecondary serving cell configured in the UE can be ordered by an RRCconnection reconfiguration message. The RRC connection reconfigurationprocedure includes a process in which the eNB sends an RRC connectionreconfiguration message to the UE and the UE sends an RRC connectionre-establishment-complete message to the eNB.

The eNB configures a TAG for the serving cell configured in the UE atstep S510. A TAG configuration between the serving cells may beperformed in a cell-specific way according to a CA condition. Forexample, if the serving cell of a specific frequency band is providedthrough an FSR or a Remote Radio Head (RRH), the serving cell of thespecific frequency band and the serving cell of a frequency banddirectly served by an eNB can be configured so that they always belongto different TAGs in relation to all MSs within the service coverage ofthe eNB.

i) If the eNB determines that the same timing advance value as that of aprimary serving cell can be applied to the added secondary serving cell,the eNB configures the added secondary serving cell so that it has thesame TAG as the primary serving cell. In this case, a process of sendingTAG configuration information, such as the step S515, may not beperformed. Here, if the UE receives an activation indicator for theadded secondary serving cell and uplink scheduling information withoutreceiving TAG configuration information, the UE determines that theadded secondary serving cell has been configured to have the same TAG asthe primary serving cell.

ii) If the eNB determines that the same timing advance value as that ofa primary serving cell cannot be applied to the added secondary servingcell, the eNB configures an sTAG including the added secondary servingcell. A TAG ID to identify each TAG is assigned to the TAG. Here, theeNB may selectively assign the TAG ID to the sTAG. For example, if theeNB confirms that the sTAG including the added secondary serving cell isdifferent from existing configured TAGs, the eNB may assign the TAG IDto the sTAG before obtaining uplink synchronization through the randomaccess procedure. For another example, if the eNB determines that theadded secondary serving cell cannot be included in an existingconfigured TAG or does not know that the added secondary serving cell isincluded in what TAG, the eNB may not assign the TAG ID to the sTAGuntil it obtains uplink synchronization through the random accessprocedure. In this case, after the UE obtains uplink synchronization,the eNB can send TAG configuration information to the UE, and the UE canobtain the TAG ID of a corresponding sTAG.

The eNB performs an RRC connection reconfiguration procedure for sendingTAG configuration information to the UE at step S515. The TAGconfiguration information can have a format including TAG ID informationfor each secondary serving cell. More particularly, uplink configurationinformation about each secondary serving cell can include TAG IDinformation. In some embodiments, the TAG configuration information canhave a format for mapping a serving cell index ‘ServCellIndex’ assignedto each serving cell or a secondary serving cell index ‘ScellIndex’assigned to only secondary serving cells. For example, a pTAG can beconfigured like {ServCellIndex=‘1’, ‘2’ }, an sTAG1 can be configuredlike {ServCellIndex=‘3’, ‘4’ } or a pTAG can be configured like{ScellIndex=‘1’, ‘2’}, and an sTAG1 can be configured like{SCellIndex=‘3’, ‘4’}. A primary serving cell does not haveconfiguration information because a serving cell index is ‘0’ and a TAGID=0. Furthermore, if there is TAG ID information in secondary servingcells, the secondary serving cells may mean serving cells within a pTAGor may mean serving cells within an independent sTAG different from allTAGs.

TAG configuration information can further include information about arepresentative serving cell within each TAG. The representative servingcell is a serving cell capable of performing a random access procedurefor maintaining and achieving uplink synchronization within each TAG andof being used as a timing reference cell. Unlike in the aboveembodiment, if TAG configuration information does not include arepresentative serving cell, UE by itself can select a representativeserving cell within each TAG. In one embodiment, UE can select a servingcell on which a random access procedure has been most recently orderedby an eNB or on which a random access procedure has been successfullycompleted, from among serving cells on which random access procedureshave been ordered by the eNB, as a representative serving cell. Inanother embodiment, UE can select a serving cell in which parameters fora random access procedure have been set when an eNB configures asecondary serving cell as a representative serving cell. If the numberof serving cells complying with a condition on a representative servingcell is plural or a representative serving cell has been deactivated, UEcan set a secondary serving cell having the lowest secondary servingcell index as a representative serving cell.

If the eNB determines to schedule a specific secondary serving cell, theeNB sends an activation indicator for activating the specific secondaryserving cell to the UE at step S520.

If uplink synchronization is not obtained from a specific sTAG, the UEhas to obtain a timing advance value to be adjusted in relation to thespecific sTAG. This adjustment can be implemented by a random accessprocedure ordered by the eNB at step S525.

The random access procedure on the activated secondary serving cellwithin the sTAG can be started by a PDCCH order transmitted by the eNB.Only a secondary serving cell including a timing reference designatedwithin an sTAG may become a secondary serving cell which can receive aPDCCH order, or all secondary serving cells in which an RACH has beenconfigured may become the secondary serving cell which can receive aPDCCH order.

The eNB performs control so that the UE performs two or more randomaccess procedures at the same time. The simultaneous execution of randomaccess procedures includes a first case where two or more random accessprocedures are synchronized with each other and performed at the sametime and a second case where two or more random access procedures areperformed at the same time in some of the time when the random accessprocedures are performed. For example, the second case includes a casewhere when UE performs a random access procedure on a primary servingcell, a random access procedure is started through a secondary servingcell (i.e., a PDCCH order is received) during the time when the UE waitsfor a Random Access Response (RAR) message. Here, the time when the UEwaits for the RAR message may include or may not include a period inwhich an RAR message can be determined to be retransmitted by the UE.

If the eNB determines that it has not secured information enough to mapa specific secondary serving cell to a specific TAG although it usesexisting information within a network and/or assistant information(e.g., location information, an RSRP, and an RSRQ) received from UE, theeNB sets the specific secondary serving cell as a new sTAG and obtainsthe uplink timing advance value through a random access procedure.

In response to the RAR message received from the eNB, the UE determinesthat the random access procedure has been successfully completed andupdates the timing advance value of the secondary serving cell at stepS530. The RAR message can be included in an RAR MAC Protocol Data Unit(PDU) that is included in and received from a PDSCH indicated by a PDCCHscrambled into a Random Access-Radio Network Temporary Identifier(RA-RNTI) and then transmitted or may be received in the form of a MACControl Element (CE) within a MAC PDU that is included in and receivedfrom a PDSCH indicated by a PDCCH scrambled into a C-RNTI.

If the RAR message is received in the form of the MAC CE, the RARmessage may be called an ‘extended TAC MAC CE’. In this case, the RARmessage can include a TA value and a TAG ID or a secondary serving cellindex.

The RRC connection reconfiguration procedure S505 for configuring asecondary serving cell and the procedure S515 for sending TAGconfiguration information for configuring a TAG are illustrated as beingseparately performed in FIG. 2, but this is only illustrative. Secondaryserving cell configuration information and TAG configuration informationmay be included in one RRC connection reconfiguration message. FIG. 3shows a process of sending secondary serving cell configurationinformation and TAG configuration information through one RRC connectionreconfiguration procedure. The procedure of FIG. 3 differs from theprocedure of FIG. 2 in that both secondary serving cell configurationinformation and TAG configuration information are transmitted to UEaccording to one RRC connection reconfiguration procedure at step S610and the UE performs the reconfiguration of a secondary serving cell andthe configuration of a TAG at once. That is, TAG configurationinformation is also transmitted in an RRC connection reconfigurationprocedure for sending secondary serving cell configuration information.

For example, the secondary serving cell configuration information mayinclude the TAG configuration information. For example, the secondaryserving cell configuration information may be an index regarding asecondary serving cell added to UE and the identifier (ID) of a TAG towhich the secondary serving cell having the index belongs. For anotherexample, the TAG configuration information may include the secondaryserving cell configuration information. For example, the TAGconfiguration information may include the TAG ID of each TAG configuredin UE, the index of a serving cell belonging to each TAG, the index of asecondary serving cell added to a specific TAG, and TAT parameters. TheTAG configuration information may not be removed although a serving cellbelonging to a corresponding TAG is not present. In other words,configuration information about a specific TAG within the TAGconfiguration information may include only a TAG ID and TAT parameters.

An RRC connection reconfiguration message transmitted from the eNB tothe UE at the step S610 may be a first RRC reconfiguration messagereceived right after the RRC connection reconfiguration procedure hasbeen successfully performed or may be other RRC reconfigurationmessages. The remaining steps S600, S605, S615, S620, and S625 are thesame as those of FIG. 2, and a detailed description thereof is omitted.

Referring back to FIG. 2, the random access procedure at the step S525can be performed by, for example, a procedure of FIG. 4.

FIG. 4 is a flowchart illustrating a method of performing random accessin accordance with an example of the present invention.

Referring to FIG. 4, an eNB sends a PDCCH order, ordering the start ofthe random access procedure regarding a secondary serving cellconfigured in UE, to the UE at step S700. Here, the secondary servingcell may be a secondary serving cell on which uplink synchronization isdetermined to be needed by the eNB.

For example, in the case of a non-contention-based random accessprocedure, the eNB selects one of pre-agreed dedicated random accesspreambles, from among all available random access preambles, and sendsRA preamble assignment information including the index of the selectedrandom access preamble and information about available time/frequencyresources to the UE through the PDCCH order. This is because the eNB hasto assign a dedicated random access preamble without a possiblecollision to the UE for the non-contention-based random accessprocedure.

For example, if the random access procedure is performed during ahandover process, the UE can obtain a dedicated random access preamblefrom a handover command message. For another example, if the randomaccess procedure is performed at the request of the eNB (i.e., inresponse to the PDCCH order), the UE can obtain a dedicated randomaccess preamble through a PDCCH, that is, physical layer signaling. Inthis case, the physical layer signaling has a Downlink ControlInformation (DCI) format 1A and can include fields shown in Table 1.

TABLE 1 A Carrier Indicator Field (CIF) - 0 or 3 bits. a flag foridentifying formats 0/1A - 1 bit (indicates format 0 in the case of 0and format 1A in the case of 1) If format 1A CRC is scrambled into aC-RNTI and the remaining fields are set as follows, the format 1A isused for a random access procedure started by a PDCCH order. Below- Alocalized/distributed) VRB assignment flag - 1 bit. Set to 0. Resourceblock assignment - ┌ log₂(N_(RB) ^(DL)(N_(RB) ^(DL) + 1)/2 ┐ bits. Allbits are set to 1 A preamble index - 6 bits A PRACH mask index (maskIndex) - 4 bits All the remaining bits of the format 1A for thetemporary scheduling assignment of one PDSCH codeword are set to 0.

Referring to Table 1, the preamble index is an index indicating onepreamble selected from pre-agreed dedicated random access preambles forthe non-contention-based random access procedure, and the PRACH maskindex is information about available time/frequency resources. Theinformation about available time/frequency resources is differentdepending on a Frequency Division Duplex (FDD) system and a TimeDivision Duplex (TDD) system as in Table 2.

TABLE 2 PRACH MASK INDEX PERMITTED PRACH (FDD) PERMITTED PRACH (TDD) 0All All 1 PRACH RESOURCE INDEX 0 PRACH RESOURCE INDEX 0 2 PRACH RESOURCEINDEX 1 PRACH RESOURCE INDEX 1 3 PRACH RESOURCE INDEX 2 PRACH RESOURCEINDEX 2 4 PRACH RESOURCE INDEX 3 PRACH RESOURCE INDEX 3 5 PRACH RESOURCEINDEX 4 PRACH RESOURCE INDEX 4 6 PRACH RESOURCE INDEX 5 PRACH RESOURCEINDEX 5 7 PRACH RESOURCE INDEX 6 RESERVED 8 PRACH RESOURCE INDEX 7RESERVED 9 PRACH RESOURCE INDEX 8 RESERVED 10 PRACH RESOURCE INDEX 9RESERVED 11 All even-numbered PRACH All even-numbered PRACHopportunities within time opportunities wihtihn time domain, a firstPRACH resource domain, a first PRACH resource index wihtin a subframeindex wihtin a subframe 12 All odd-numbered PRACH All odd-numbered PRACHopportunities within time opportunities within time domain, a firstPRACH resource domain, a first PRACH resource index wihtin a subframeindex wihtin a subframe 13 RESERVED a first PRACH resource index wihtina subframe 14 RESERVED a second PRACH resource index wihtin a subframe15 RESERVED a third PRACH resource index wihtin a subframe

For another example, in the case of a contention-based random accessprocedure, the eNB sets a preamble index within the RA preambleassignment information to ‘000000’ and sends the RA preamble assignmentinformation to the UE. The UE randomly selects one of contention-basedrandom access preambles, sets a value of the PRACH mask index to ‘0’,and performs a contention-based procedure. Furthermore, the RA preambleassignment information can be transmitted to the UE through a higherlayer message (e.g., Mobility Control Information (MCI) within ahandover command), such as RRC signaling.

The UE sends a random access preamble on the secondary serving celldesignated at the step S700 to the eNB at step S705. The random accesspreamble may be transmitted on a representative serving cell within aTAG to which the secondary serving cell belongs. A representativeserving cell is a serving cell that has been selected to send the randomaccess preamble within the TAG configured in the UE. The representativeserving cell can be selected for each TAG. Furthermore, the UE may sendthe random access preamble on a representative serving cell within anyone TAG, from among a plurality of TAGs, or may send the random accesspreamble on two or more representative serving cells within respectiveTAGs. For example, it is assumed that TAGs configured in the UE are aTAG1 and a TAG2, the TAG1=(a first serving cell, a second serving cell,a third serving cell), and the TAG2={a fourth serving cell, a fifthserving cell}. If the representative serving cell of the TAG1 is thesecond serving cell and the representative serving cell of the TAG2 isthe fifth serving cell, the UE sends an assigned dedicated random accesspreamble to the eNB through the second serving cell or the fifth servingcell.

The representative serving cell may also be called a special servingcell (special SCell), a reference serving cell (reference SCell), or atiming reference serving cell (or timing reference cell).

The eNB sends an RAR message to the UE at step S710. The RAR messageincludes a timing advance value. When the eNB successfully receives therandom access preamble, the eNB can check that what UE has sent therandom access preamble through what serving cell on the basis of thereceived random access preamble and time/frequency resources. Inparticular, if UE starts a random access procedure for a secondaryserving cell in response to the PDCCH order of the eNB, the UE hasalready secured an identifier unique to the UE, for example, a C-RNTI,from a primary serving cell. Accordingly, the eNB can send an RARmessage to the UE by using the C-RNTI of the UE if necessary. Here, touse the C-RNTI includes scrambling a PDCCH, indicating a PDSCH to whichthe RAR message has been mapped, into the C-RNTI.

In another embodiment, the eNB may send the RAR message on the primaryserving cell by using the Random Access-Radio Network TemporaryIdentifier (RA-RNTI) of the UE. In response to the RAR message receivedfrom the eNB, the UE determines that the random access procedure hasbeen successfully completed.

If a secondary serving cell is added to or released from the UE, anexisting TAG can be updated by the UE or the eNB. For example, it isassumed that TAGs configured in the UE are a TAG1 and a TAG2, theTAG1={a first serving cell, a second serving cell}, and the TAG2={afourth serving cell}. If a third secondary serving cell has to be addedin order to extend the bandwidth of the UE, the eNB sends secondaryserving cell configuration information for adding the third secondaryserving cell to the UE by using an RRC connection reconfigurationprocedure. If the third secondary serving cell has the same timingadvance value as the TAG1, the third secondary serving cell is enrolledin the TAG1. Here, the eNB or the UE is updated from the TAG1 into aTAG1={the first serving cell, the second serving cell, the third servingcell}, but does not change the TAG2. In contrast, if the third secondaryserving cell has a different timing advance value from that of the TAG1or the TAG2, the third secondary serving cell belongs to a new TAG3.Accordingly, the eNB or the UE configures the new TAG3={the thirdsecondary serving cell}.

As described above, secondary serving cell configuration information andTAG configuration information have a close relationship because a changein the configuration of secondary serving cells leads to thereorganization of a TAG. The reorganization of a TAG is also related touplink synchronization because it can result in the update of a timingadvance value applied to a secondary serving cell. The reorganization ofa TAG may also be called the update, change, or reconfiguration of aTAG. The reorganization of a TAG may have the same meaning as the updateor change of TAG configuration information because UE or an eNB updatesor changes TAG configuration information.

The reorganization of a TAG includes all cases where a TAG is newlygenerated and deleted if a secondary serving cell included in the TAG ischanged. The reorganization of a TAG due to a change in theconfiguration of a secondary serving cell can include a variety ofembodiments. For example, in order to reorganize a TAG, an eNB may sendsignaling related to the reorganization of the TAG to UE and the UE byitself can reorganize the TAG even without signaling. Furthermore, forthe reorganization of a TAG, a message for an RRC connectionreconfiguration procedure may be used and signaling for a random accessprocedure may be used. Furthermore, a message for the reorganization ofa TAG can have a variety of formats. The reorganization of a TAGaccording to a variety of embodiments and corresponding uplinksynchronization are described below. First, a procedure for reorganizinga TAG when a secondary serving cell is released is described below.

(1) A Procedure for Reorganizing a TAG when a Secondary Serving Cell isReleased

FIG. 5 is a flowchart illustrating a method of reorganizing a TAG inaccordance with an example of the present invention.

Referring to FIG. 5, an eNB determines to release a secondary servingcell configured in UE at step S800. For example, if a frequency bandnecessary for UE is reduced or connection to secondary serving cellsconfigured by a serving eNB is released in a target eNB after ahandover, the eNB can determine to release a secondary serving cell. IfUE releases all secondary serving cells owing to the start of an RRCconnection reconfiguration procedure due to a Radio Link Failure (RLF),the UE resets or removes all pieces of TAG configuration information.When the TAG configuration information is reset, TAG ID informationremains intact, but a TA value within each TAG is set to ‘0’,information about a serving cell included in each TAG is removed, and aTAT parameter is set to ‘infinity’.

The eNB reorganizes a TAG at step S805. Here, the reorganization of theTAG corresponds to the update of the TAG to which the released secondaryserving cell belonged. For example, if a TAG to which the secondaryserving cell belonged is a TAG1={a first serving cell, a second servingcell} and the secondary serving cell to be released is the secondserving cell, the eNB is updated into a TAG1={the first serving cell}.

Since the eNB has released the secondary serving cell and reorganizedthe TAG, the eNB has to inform the UE of the release of the secondaryserving cell and the reorganization of the TAG. Here, the eNB can sendonly secondary serving cell configuration information, ordered therelease of the secondary serving cell, to the UE. This is because the UEcan update the TAG so that the secondary serving cell is released fromthe TAG even without additional TAG configuration information becausethe UE is already aware that the secondary serving cell to be releasedbelongs to what TAG.

Accordingly, the eNB performs an RRC connection reconfigurationprocedure for releasing the secondary serving cell at step S810. Forexample, in the RRC connection reconfiguration procedure at the stepS810, the secondary serving cell configuration information for releasingthe secondary serving cell and information about the configuration ofthe reorganized TAG (hereinafter abbreviated to ‘reorganized TAGconfiguration information’) may be included in different RRC connectionreconfiguration messages as in FIG. 2. In this case, the RRC connectionreconfiguration procedure is performed twice. Here, the sequence of thestep S805 may be performed in the RRC connection reconfigurationprocedure for sending the reorganized TAG configuration information atthe step S810.

For another example, in the RRC connection reconfiguration procedure atthe step S810, the secondary serving cell configuration information andthe reorganized TAG configuration information may be included in thesame RRC connection reconfiguration message as in FIG. 3. In this case,the RRC connection reconfiguration procedure is performed once. That is,the reorganized TAG configuration information is also transmitted in theexisting RRC connection reconfiguration procedure for sending thesecondary serving cell configuration information. Here, the reorganizedTAG configuration information may be included in the secondary servingcell configuration information and transmitted or may be transmittedthrough an additional field different from that of the secondary servingcell configuration information. If the reorganized TAG configurationinformation is transmitted through an additional field, the reorganizedTAG configuration information may be represented by, for example, apTAG={1, 3} and an sTAG[TAG ID=1]={2, 4}. Here, the pTAG={1, 3} means aprimary serving cell and serving cells in which a secondary servingcell1 and a secondary serving cell3 form the pTAG.

For yet another example, the RRC connection reconfiguration procedure atthe step S810 may not include the reorganized TAG configurationinformation. This means that configuration information does not includeTAG configuration information.

The secondary serving cell configuration information for releasing thesecondary serving cell is sCellToReleaseList and can be defined as inthe following table.

TABLE 3 RRCConnectionReconfiguration IEs ::= SEQUENCE {sCellToReleaseList SCellToReleaseList OPTIONAL, -- Need ONsCellToAddModList SCellToAddModList OPTIONAL, -- Need ONnonCriticalExtension SEQUENCE { } OPTIONAL -- Need OP }SCellToReleaseList ::= SEQUENCE (SIZE (1..maxSCell)) OF SCellIndex

Referring to Table 3, the RRC connection reconfiguration message‘RRCConnectionReconfiguration IEs’ include sCellToReleaseList, that is,the secondary serving cell configuration information for releasing thesecondary serving cell. The size of sCellToReleaseList can be set to 1to a maximum number of secondary serving cells ‘maxScell, andsCellToReleaseList indicates the index of a secondary serving cell‘SCellIndex’ to be released.

If the RRC connection reconfiguration message including the secondaryserving cell configuration information for releasing the secondaryserving cell is received, the UE releases the secondary serving cellfrom a TAG to which the secondary serving cell to be released belongsand reorganizes the TAG at step S815. The UE can perform thereorganization of the TAG even without TAG configuration information. Inthis aspect, the RRC connection reconfiguration message at the step S810has a function of releasing a secondary serving cell and also ordering aTAG to be reorganized. If a pTAG and an sTAG are configured in the UEand the secondary serving cell of the sTAG is released when onesecondary serving cell is included in the sTAG, the TAG ID of the sTAGis also removed due to the reorganization of the TAG. In contrast, ifonly a pTAG is configured in the UE, the reorganization of a TAGincluding the removal of the pTAG is not performed because although asecondary serving cell is released from the pTAG because the pTAGnecessarily includes a primary serving cell. As described above, thereorganization of the TAG can be performed when both a pTAG and an sTAGare configured in the UE.

As described above, a procedure can be simplified and a TAG can bereorganized more rapidly because TAG configuration information for thereorganization of the TAG does not need to be separately transmitted.

A procedure for reorganizing a TAG when a secondary serving cell isadded is described below.

(2) A Procedure for Reorganizing a TAG when a Secondary Serving Cell isAdded is Described Below

In releasing a secondary serving cell, UE and an eNB do not need tofurther maintain uplink synchronization with a secondary serving cell tobe released. Accordingly, a timing advance value is also not necessary.In adding a secondary serving cell, however, an eNB or UE has toreorganize a TAG to which the added secondary serving cell belongs andknow the timing advance value of the added secondary serving cell forthe reorganization.

The timing advance value of the added secondary serving cell can bebasically obtained on the basis of a random access procedure. If theadded secondary serving cell can be mapped to an already defined TAG, arandom access procedure for obtaining the timing advance value does notneed to be performed. Here, the case where the added secondary servingcell can be mapped to the already defined TAG can include a case wherethe added secondary serving cell has the same timing advance value asthe already defined TAG. Furthermore, the case where the added secondaryserving cell can be mapped to the already defined TAG may include a casewhere an eNB is already aware of the timing advance value of the addedsecondary serving cell.

If the eNB is already aware of the timing advance value of the addedsecondary serving cell, the eNB can be aware that the added secondaryserving cell has to be reorganized in what TAG. That is, the eNB candetermine a TAG. For example, it is assumed that a TAG1 and a TAG2 areconfigured in UE, the timing advance value of the TAG1 is TA1, and thetiming advance value of the TAG2 is TA2. If an eNB is aware that anadded secondary serving cell has the timing advance value=TA2, the eNBreorganizes the added secondary serving cell into the TAG2. If the eNBis aware that the added secondary serving cell has a timing advancevalue=TA3, the eNB reorganizes the added secondary serving cell into anew TAG3.

In contrast, if an eNB is not aware of the timing advance value of anadded secondary serving cell, the eNB cannot determine a TAG. In thiscase, the eNB can set the TAG ID of the added secondary serving cell bydefault. The TAG ID set by default may also be called a temporary TAGID. Subsequently, the eNB can reorganize the added secondary servingcell into a specific TAG. That is, in the contents of reorganized TAGconfiguration information, the reorganized TAG configuration informationcan include a definite TAG ID or a temporary TAG ID. The temporary TAGID is set to a default value. Here, the default value can be, forexample, 0, and the temporary TAG ID may not have any value.

A method in which an eNB informs UE of information about theconfiguration of a TAG reorganized by the addition of a secondaryserving cell can be implemented by using a variety of embodiments. Forexample, in a method of sending TAG configuration information, an eNBcan send secondary serving cell configuration information, ordering theaddition of a secondary serving cell, and reorganized TAG configurationinformation to UE through an RRC connection reconfiguration procedure.Here, the secondary serving cell configuration information and the TAGconfiguration information may be transmitted through one RRC connectionreconfiguration procedure or may be transmitted through different RRCconnection reconfiguration procedures.

A case where an eNB does not need an additional random access procedurein order to map an added secondary serving cell to a TAG is firstdescribed below.

(2-1) When a Random Access Procedure is not Necessary in Order toReorganize a TAG

FIG. 6 is a flowchart illustrating a method of reorganizing a TAG inaccordance with another example of the present invention.

Referring to FIG. 6, an eNB determines to add a secondary serving cellat step S900. For example, if a bandwidth supported for UE is increasedor the new cell of a target eNB is accessed due to a handover, the eNBcan determine to add the secondary serving cell. The reorganization of aTAG due to the addition of the secondary serving cell can include twocases. In the first case, an existing TAG configured in the UE remainsintact, and the secondary serving cell is added to an existing pTAG orany one of sTAGs. In the second case, a new TAG is configured inaddition to a TAG already configured in the UE, and the secondaryserving cell is added to the new TAG. In either case, the addedsecondary serving cell needs to be mapped to the TAG. Furthermore, theeNB does not perform an additional random access procedure because it isaware of the timing advance value of the added secondary serving cell.That is, the eNB can directly reorganize a TAG and send reorganized TAGconfiguration information without an additional random access procedure.

The eNB reorganizes a TAG in response to the added secondary servingcell at step S905. The reorganization of the TAG includes adding thesecondary serving cell to an existing TAG or configuring a new TAGincluding the added secondary serving cell.

The eNB performs an RRC connection reconfiguration procedure for addingthe secondary serving cell at step S910. For example, in the RRCconnection reconfiguration procedure at the step S910, the secondaryserving cell configuration information for adding the secondary servingcell and the reorganized TAG configuration information may be includedin different RRC connection reconfiguration messages (refer to the stepsS505 and S515) as in FIG. 2. In this case, the RRC connectionreconfiguration procedure is performed twice. Here, the sequence of thestep S905 may be performed in the RRC connection reconfigurationprocedure for sending the reorganized TAG configuration information atthe step S910. Meanwhile, the reorganized TAG configuration informationmay be represented by, for example, a pTAG={1, 3} and an sTAG[TAGID=1]={2, 4}.

For another example, in the RRC connection reconfiguration procedure atthe step S910, the secondary serving cell configuration information foradding the secondary serving cell and the reorganized TAG configurationinformation may be included in the same RRC connection reconfigurationmessage as in FIG. 3. In this case, the RRC connection reconfigurationprocedure is performed once. That is, in the existing RRC connectionreconfiguration procedure for sending the secondary serving cellconfiguration information, the TAG configuration information is alsotransmitted. Here, the reorganized TAG configuration information may beincluded in the secondary serving cell configuration information andtransmitted or may be transmitted through an additional field differentfrom that of the secondary serving cell configuration information. Ifthe reorganized TAG configuration information is transmitted through anadditional field, the reorganized TAG configuration information may berepresented by, for example, a pTAG={1, 3} and an sTAG[TAG ID=1]={2, 4}.

The reorganized TAG configuration information includes information forassigning the added secondary serving cell to a new TAG ID or assigningthe added secondary serving cell to an existing TAG ID. The secondaryserving cell configuration information for releasing the secondaryserving cell is sCellToAddModList and can be defined as in the followingtable.

TABLE 4 RRCConnectionReconfiguration IEs ::= SEQUENCE {sCellToReleaseList SCellToReleaseList OPTIONAL, -- Need ONsCellToAddModList SCellToAddModList OPTIONAL, -- Need ONnonCriticalExtension SEQUENCE { } OPTIONAL -- Need OP }SCellToAddModList ::= SEQUENCE (SIZE (1..maxSCell)) OF SCellToAddModSCellToAddMod ::= SEQUENCE { sCellIndex SCellIndex, cellIdentificationSEQUENCE { physCellId PhysCellId, dl-CarrierFreq ARFCN-ValueEUTRA }OPTIONAL, -- Cond SCellAdd radioResourceConfigCommonSCellRadioResourceConfigCommonSCell OPTIONAL, -- Cond SCellAddradioResourceConfigDedicatedSCell RadioResourceConfigDedicatedSCellOPTIONAL, -- Cond SCellAdd2 ... }

Referring to Table 4, the RRC connection reconfiguration message‘RRCConnectionReconfiguration IEs’ includes sCellToAddModList andSCellToAddMod, that is, pieces of secondary serving cell configurationinformation for adding a secondary serving cell. The size ofsCellToAddModList can be set to 1 to a maximum number of secondaryserving cells ‘maxScell’, and sCellToAddModList indicates the index ofthe secondary serving cell to be added ‘SCellIndex’. SCellToAddModincludes the index of an added secondary serving cell ‘sCellIndex’.SCellToAddMod can further include a TAG ID regarding the added secondaryserving cell.

When the RRC connection reconfiguration message including the secondaryserving cell configuration information for adding the secondary servingcell is received, the UE reorganizes the TAG at step S915. The UEreorganizes the TAG based on the TAG configuration information includedin the secondary serving cell configuration information.

A case where an eNB needs an additional random access procedure in orderto map an added secondary serving cell to a TAG is described below. Thiscase corresponds to a case where the eNB is not aware of the timingadvance value of the added secondary serving cell.

(2-2) When a Random Access Procedure is Necessary to Reorganize a TAG

An eNB can obtain a timing advance value regarding an added secondaryserving cell by performing a random access procedure in order toreorganize a TAG. Before obtaining the timing advance value, the eNB hasto configure the added secondary serving cell in UE and perform an RRCconnection reconfiguration procedure for reorganizing the TAG.Meanwhile, when reorganizing the TAG, the eNB may not be aware that theadded secondary serving cell belongs to what TAG or may not assignanother TAG ID to the UE because a maximum number of TAG IDs havealready been assigned to the UE. In this case, how a TAG regarding theadded secondary serving cell will be defined becomes ambiguous.Accordingly, there is a need for a criterion for determining thecontents of reorganized TAG configuration information. For example, theeNB may define a temporary TAG ID and map the added secondary servingcell to the temporary TAG ID. In this case, reorganized TAGconfiguration information includes the temporary TAG ID. For example,the eNB can determine a TAG ID having the lowest index, from among theremaining TAG IDs other than the IDs of TAGs now configured in the UE,as the temporary TAG ID. For another example, the eNB may determine aspecific one of the remaining TAG IDs other than the IDs of TAGs nowconfigured in the UE as the temporary TAG ID.

For another example, the eNB may not define an additional TAG ID for theadded secondary serving cell. In this case, the reorganized TAGconfiguration information may include a TAG ID set to ‘Null’, or thereorganized TAG configuration information is not transmitted.

A case where the reorganized TAG configuration information includes thetemporary TAG ID is described below.

(2-2-1) a Case where Reorganized TAG Configuration Information Includesa Temporary TAG ID

The present embodiment includes a first embodiment in which TAGconfiguration information is defined in an additional field differentfrom that of secondary serving cell configuration information and asecond embodiment in which TAG configuration information is included insecondary serving cell configuration information. The first embodimentis first described below.

FIG. 7 is a flowchart illustrating a method of reorganizing a TAG inaccordance with yet another example of the present invention.

Referring to FIG. 7, an eNB determines to add a secondary serving cellat step S1000. For example, if a bandwidth supported for UE is increasedor the new cell of a target eNB is accessed due to a handover, the eNBcan determine to add the secondary serving cell.

The eNB and the UE first perform an RRC connection reconfigurationprocedure for adding the secondary serving cell at step S1005. An RRCconnection reconfiguration message at the step S1005 includes secondaryserving cell configuration information. Next, the eNB and the UE performan RRC connection reconfiguration procedure for reorganizing a TAG atstep S1010. An RRC connection reconfiguration message at the step S1010includes TAG configuration information. Furthermore, the TAGconfiguration information indicates a temporary TAG ID.

If the eNB tries to schedule the added secondary serving cell, the eNBsends an activation indicator for activating the added secondary servingcell to the UE at step S1015.

The UE has to obtain a timing advance value to be adjusted in relationto the added secondary serving cell because it has not achieved uplinksynchronization regarding the added secondary serving cell. This can beimplemented by a random access procedure ordered by the eNB.

The eNB sends a PDCCH order, ordering the start of the random accessprocedure regarding the secondary serving cell additionally configuredin the UE, to the UE at step S1020.

The UE sends a random access preamble to the eNB on the added secondaryserving cell at step S1025. The random access procedures at the stepsS1020 and S1025 can be performed as in FIG. 4.

The eNB can obtain a timing advance value regarding the added secondaryserving cell through the random access procedure and performs TAGreorganization for mapping the added secondary serving cell to aspecific TAG based on the timing advance value at step S1030.

The eNB performs an RRC connection reconfiguration procedure forreorganizing the existing TAG at step S1035. The RRC connectionreconfiguration procedure for reorganizing the TAG includes a process inwhich the eNB sends an RRC connection reconfiguration message, includingthe reorganized TAG configuration information, to the UE and the UEsends an RRC connection re-establishment-complete message to the eNBafter the TAG is reorganized.

In accordance with a common random access procedure, the eNB has to sendan RAR message in response to the random access preamble. However, therandom access procedures at the steps S1025 and S1030 are additionallyused to map the added secondary serving cell to the TAG and reorganizethe TAG. Accordingly, a step of sending the RAR message may be omitted,and the RRC connection reconfiguration message for reorganizing the TAGcan order the TAG to be reorganized and also mean the success or stop ofthe random access procedure. The present embodiment, however, mayinclude a step of sending an RAR message. In this case, the step S1035can be performed after the eNB sends the RAR message to the UE.

When receiving the RRC connection reconfiguration message forreorganizing the TAG during the random access procedure, the UEdetermines that the random access procedure has been successful or thatthe random access procedure has been stopped by an order of the eNB andterminates the random access procedure. Next, the UE reorganizes the TAGbased on the reorganized TAG configuration information at step S1040.For example, the UE maps the secondary serving cell to which thetemporary TAG ID has been assigned to a TAG having an ID assigned basedon the reorganized TAG configuration information. Here, the TAG havingthe assigned ID may be a pTAG or an sTAG already configured in the UE ormay be a new sTAG.

The second embodiment in which the TAG configuration information isincluded in the secondary serving cell configuration information isdescribed below.

FIG. 8 is a flowchart illustrating a method of reorganizing a TAG inaccordance with still yet another example of the present invention.

Referring to FIG. 8, an eNB determines to add a secondary serving cellat step S1100. For example, if a bandwidth supported for UE is increasedor the new cell of a target eNB is accessed due to a handover, the eNBcan determine to add the secondary serving cell.

The eNB and the UE first perform an RRC connection reconfigurationprocedure for adding the secondary serving cell and reorganizing a TAGat step S1105. An RRC connection reconfiguration message at the stepS1105 includes secondary serving cell configuration information, and thesecondary serving cell configuration information includes TAGconfiguration information. Furthermore, the TAG configurationinformation indicates a temporary TAG ID.

If the eNB tries to schedule the added secondary serving cell, the eNBsends an activation indicator for activating the added secondary servingcell to the UE at step S1110.

The UE has to obtain a timing advance value to be adjusted in relationto the added secondary serving cell because it has not achieved uplinksynchronization regarding the added secondary serving cell. This can beimplemented by a random access procedure ordered by the eNB.

The eNB sends a PDCCH order, ordering the start of the random accessprocedure regarding the secondary serving cell additionally configuredin the UE, to the UE at step S1115.

The UE sends a random access preamble to the eNB on the added secondaryserving cell at step S1120. The random access procedures at the stepsS1115 and S1120 can be performed as in FIG. 4.

The eNB can obtain a timing advance value regarding the added secondaryserving cell through the random access procedure and performs TAGreorganization for mapping the added secondary serving cell to aspecific TAG based on the timing advance value at step S1125.

The eNB performs an RRC connection reconfiguration procedure for thechange of the secondary serving cell and the reorganization of the TAGat step S1130. The RRC connection reconfiguration procedure for thechange of the secondary serving cell and the reorganization of the TAGincludes a process in which the eNB sends an RRC connectionreconfiguration message to the UE and the UE sends an RRC connectionre-establishment-complete message to the eNB after reorganizing the TAG.Here, the RRC connection reconfiguration message includes secondaryserving cell configuration information on which the eNB orders thesecondary serving cell to be changed, and the secondary serving cellconfiguration information includes reorganized TAG configurationinformation.

In accordance with a common random access procedure, the eNB has to sendan RAR message in response to the random access preamble. However, therandom access procedures at the steps S1120 and S1125 are additionallyused to map the added secondary serving cell to the TAG and reorganizethe TAG. Accordingly, a step of sending the RAR message may be omitted,and the RRC connection reconfiguration message for reorganizing the TAGcan order the TAG to be reorganized and also mean the success or stop ofthe random access procedure. The present embodiment, however, mayinclude a step of sending an RAR message. In this case, the step S1130can be performed after the eNB sends the RAR message to the UE.

In response to the RRC connection reconfiguration message receivedduring the random access procedure, the UE determines that the randomaccess procedure is successful or that the random access procedure hasbeen stopped by an order of the eNB and terminates the random accessprocedure. Next, the UE reorganizes the TAG based on the reorganized TAGconfiguration information at step S1135. For example, the UE maps thesecondary serving cell to which the temporary TAG ID has been assignedto a TAG having an ID assigned based on the reorganized TAGconfiguration information. Here, the TAG of the assigned ID may be apTAG or an sTAG already configured in the UE or may be a new sTAG.

FIGS. 7 and 8 illustrate embodiments in which an eNB directly informs UEof the reorganization of a TAG by using an RRC connectionreconfiguration procedure. In accordance with another embodiment,however, the eNB may inform the UE of a timing advance value through anRAR message because a random access procedure is already in progress. Inthis case, the UE is not directly informed of reorganized TAGconfiguration information, but the UE by itself can reorganize a TAGbased on the timing advance value. In this sense, it can be seen thatthe eNB implicitly informs the UE of the reorganized TAG configurationinformation.

FIG. 9 is a flowchart illustrating a method of reorganizing a TAG inaccordance with further yet another example of the present invention.

Steps S1200 to S1225 of FIG. 9 are the same as the steps S1100 to S1125of FIG. 8, and thus a detailed description thereof is omitted.

An eNB calculates a timing advance value regarding an added secondaryserving cell when receiving a random access preamble and sends an RARmessage indicative of the timing advance value to UE at step S1230.Here, the RAR message is a MAC message, and the timing advance value maybe indicated by a field within a MAC Random Access Response (RAR). Inthis case, the RAR message is mapped to a PDSCH indicated by a PDCCHthat is scrambled into a Random Access (RA)-Radio Network TemporaryIdentifier (RNTI) for identifying the UE in a random access procedureand is then transmitted. The PDCCH scrambled into the RA-RNTI istransmitted on a primary serving cell which provides a common searchspace.

In an embodiment, the RAR message may be indicated by a MAC ControlElement (CE). The field indicative of the timing advance value is calleda Timing Advance Command (TAC) field. In this case, the RAR message ismapped to a PDSCH indicated by a PDCCH scrambled into a Cell (C)-RNTIfor identifying the UE in a UE-specific space and then transmitted. ThePDCCH scrambled into the C-RNTI can be transmitted on a secondaryserving cell which provides a UE-specific search space.

In response to the RAR message, the UE performs TAG reorganization atstep S1235. As an example of the TAG reorganization, if there is a TAGhaving the same timing advance value as that of an existing TAG (a pTAGor an sTAG), the UE maps the added secondary serving cell to thecorresponding TAG.

As another example of the TAG reorganization, if the timing advancevalue is different from a timing advance value applied to an existingTAG (a pTAG or an sTAG) and the number of TAGs now configured in the UEis smaller than a maximum number of TAGs that can be configured, the UEdesignates a temporary TAG ID as the TAG ID of a new sTAG and maps anadditional secondary serving cell to the TAG.

As yet another example of the TAG reorganization, if the timing advancevalue is different from a timing advance value applied to an existingTAG (a pTAG or an sTAG) and the number of TAGs now configured in the UEis the same as a maximum number of TAGs that can be configured, the UEcan perform one of the following operations. i) The UE may determinethat the timing advance value for the added secondary serving cell isnot valid and disregard the received timing advance value. ii) The UEmay deactivate the added secondary serving cell in order to preventuplink transmission within a corresponding TAG. This is because may be aproblem in uplink transmission within the TAG because a new TAG ID andthe configuration of a current TAG are not valid. iii) The UE mayrelease the configuration of the added secondary serving cell instead ofthe deactivation operation.

A case where reorganized TAG configuration information is nottransmitted is described below.

(2-2-2) when Reorganized TAG Configuration Information is notTransmitted

The meaning that reorganized TAG configuration information is nottransmitted may be i) a TAG ID=0 or ii) a TAG ID=‘Null’ or iii) may bethat TAG configuration information is not included in secondary servingcell configuration information. In the case of i), an added secondaryserving cell is mapped to the pTAG by default because the ID of a pTAGis basically 0. In the case of ii) and iii), an added secondary servingcell may be mapped to a pTAG by default or may not have been mapped toany TAG. Some embodiments are described below assuming that an addedsecondary serving cell is mapped to a pTAG by default when TAGconfiguration information is not transmitted. It is however to be notedthat each of the embodiments may be likewise applied to a case where anadded secondary serving cell is assumed not to be mapped to any TAG.

The present embodiment includes a first embodiment in which TAGconfiguration information is defined by secondary serving cellconfiguration information and an additional field and a secondembodiment in which TAG configuration information is included insecondary serving cell configuration information. The first embodimentis first described below.

FIG. 10 is a flowchart illustrating a method of reorganizing a TAG inaccordance with further yet another example of the present invention.

Referring to FIG. 10, an eNB determines to add a secondary serving cellat step S1300. For example, if a bandwidth supported for UE is increasedor the new cell of a target eNB is accessed due to a handover, the eNBcan determine to add the secondary serving cell.

The eNB and the UE first perform an RRC connection reconfigurationprocedure for adding the secondary serving cell at step S1305. An RRCconnection reconfiguration message at the step S1305 includes secondaryserving cell configuration information. The eNB and the UE do notperform an RRC connection reconfiguration procedure for reorganizing aTAG. That is, the reorganized TAG configuration information is nottransmitted.

The UE reorganizes the added secondary serving cell into a pTAG at stepS1310. That is, the added secondary serving cell is mapped to the pTAGby default.

If the eNB tries to schedule the added secondary serving cell, the eNBsends an activation indicator for activating the added secondary servingcell to the UE at step S1315.

The UE has to obtain a timing advance value to be adjusted in relationto the added secondary serving cell because it has not achieved uplinksynchronization regarding the added secondary serving cell. This can beimplemented by a random access procedure ordered by the eNB.

The eNB sends a PDCCH order, ordering the start of the random accessprocedure regarding the secondary serving cell additionally configuredin the UE, to the UE at step S1320.

The UE sends a random access preamble to the eNB on the added secondaryserving cell at step S1325. The added secondary serving cell hasbelonged to the pTAG by default. In the pTAG, only a primary servingcell is a representative serving cell which sends the random accesspreamble. However, since the added secondary serving cell is a newsecondary serving cell and the newest timing advance value can beobtained, the UE is permitted to send the random access preamble on theadded secondary serving cell. The random access procedures at the stepsS1320 and S1325 can be performed as in FIG. 4.

The eNB can obtain the timing advance value regarding the addedsecondary serving cell through the random access procedure and performsTAG reorganization for mapping the added secondary serving cell to aspecific TAG based on the timing advance value at step S1330.

The eNB performs an RRC connection reconfiguration procedure forreorganizing the TAG at step S1335. The RRC connection reconfigurationprocedure for the reorganization of the TAG includes a process in whichthe eNB sends an RRC connection reconfiguration message, includingreorganized TAG configuration information, to the UE and the UE sends anRRC connection re-establishment-complete message to the eNB afterreorganizing the TAG.

In accordance with a common random access procedure, the eNB has to sendan RAR message in response to the random access preamble. However, therandom access procedures at the steps S1325 and S1330 are additionallyused to map the added secondary serving cell to the TAG and reorganizethe TAG. Accordingly, a step of sending the RAR message may be omitted,and the RRC connection reconfiguration message for reorganizing the TAGcan order the TAG to be reorganized and also mean the success or stop ofthe random access procedure. The present embodiment, however, mayinclude a step of sending an RAR message. In this case, the step S1335can be performed after the eNB sends the RAR message to the UE.

When receiving the RRC connection reconfiguration message forreorganizing the TAG during the random access procedure, the UEdetermines that the random access procedure is successful or that therandom access procedure has been stopped by an order of the eNB andterminates the random access procedure. Next, the UE reorganizes the TAGbased on the reorganized TAG configuration information at step S1340.For example, the UE maps the secondary serving cell to which thetemporary TAG ID has been assigned to a TAG having an ID assigned basedon the reorganized TAG configuration information. Here, the TAG of theassigned ID may be a pTAG or an sTAG already configured in the UE or maybe a new sTAG.

The second embodiment in which TAG configuration information is includedin secondary serving cell configuration information is described below.

FIG. 11 is a flowchart illustrating a method of reorganizing a TAG inaccordance with further yet another example of the present invention.

Referring to FIG. 11, an eNB determines to add a secondary serving cellat step S1400. For example, if a bandwidth supported for UE is increasedor the new cell of a target eNB is accessed due to a handover, the eNBcan determine to add the secondary serving cell.

The eNB and the UE first perform an RRC connection reconfigurationprocedure for adding the secondary serving cell and reorganizing a TAGat step S1405. An RRC connection reconfiguration message at the stepS1405 includes secondary serving cell configuration information, and thesecondary serving cell configuration information includes TAGconfiguration information. Furthermore, the TAG configurationinformation includes a TAG ID set to ‘Null’.

The UE reorganizes the added secondary serving cell into a pTAG at stepS1410. That is, the added secondary serving cell is mapped to the pTAGby default.

If the eNB tries to schedule the added secondary serving cell, the eNBsends an activation indicator for activating the added secondary servingcell to the UE at step S1415.

The UE has to obtain a timing advance value to be adjusted in relationto the added secondary serving cell because it has not achieved uplinksynchronization regarding the added secondary serving cell. This can beimplemented by a random access procedure ordered by the eNB.

The eNB sends a PDCCH order, ordering the start of the random accessprocedure regarding the secondary serving cell additionally configuredin the UE, to the UE at step S1420.

The UE sends a random access preamble to the eNB on the added secondaryserving cell at step S1425. The added secondary serving cell hasbelonged to the pTAG by default. In the pTAG, only a primary servingcell is a representative serving cell which sends the random accesspreamble. However, since the added secondary serving cell is a newsecondary serving cell and the newest timing advance value can beobtained, the UE is permitted to send the random access preamble on theadded secondary serving cell. The random access procedures at the stepsS1420 and S1425 can be performed as in FIG. 4.

The eNB can obtain a timing advance value regarding the added secondaryserving cell through the random access procedure and performs TAGreorganization for mapping the added secondary serving cell to aspecific TAG based on the timing advance value at step S1430.

The eNB performs an RRC connection reconfiguration procedure forchanging the secondary serving cell and reorganizing the TAG at stepS1435. The RRC connection reconfiguration procedure for the change ofthe secondary serving cell and the reorganization of the TAG includes aprocess in which the eNB sends an RRC connection reconfiguration messageto the UE and the UE sends an RRC connection re-establishment-completemessage to the eNB after reorganizing the TAG. Here, the RRC connectionreconfiguration message includes secondary serving cell configurationinformation on which the eNB orders the secondary serving cell to bechanged, and the secondary serving cell configuration informationincludes reorganized TAG configuration information.

In accordance with a common random access procedure, the eNB has to sendan RAR message in response to the random access preamble. However, therandom access procedures at the steps S1420 and S1425 are additionallyused to map the added secondary serving cell to the TAG and reorganizethe TAG. Accordingly, a step of sending the RAR message may be omitted,and the RRC connection reconfiguration message for reorganizing the TAGcan order the TAG to be reorganized and also mean the success or stop ofthe random access procedure. The present embodiment, however, mayinclude a step of sending an RAR message. In this case, the step S1435can be performed after the eNB sends the RAR message to the UE.

In response to the RRC connection reconfiguration message receivedduring the random access procedure, the UE determines that the randomaccess procedure is successful or that the random access procedure hasbeen stopped by an order of the eNB and terminates the random accessprocedure. Next, the UE reorganizes the TAG based on the reorganized TAGconfiguration information at step S1440. For example, the UE maps thesecondary serving cell to which the temporary TAG ID has been assignedto a TAG having an ID assigned based on the reorganized TAGconfiguration information. Here, the TAG of the assigned ID may be apTAG or an sTAG already configured in the UE or may be a new sTAG.

FIGS. 10 and 11 illustrate embodiments in which an eNB directly informsUE of the reorganization of a TAG by using an RRC connectionreconfiguration procedure. In accordance with another embodiment,however, the eNB may inform the UE of a timing advance value through anRAR message because a random access procedure is already in progress. Inthis case, the UE is not directly informed of reorganized TAGconfiguration information, but the UE by itself can reorganize a TAGbased on the timing advance value. In this sense, it can be seen thatthe eNB implicitly informs the UE of the reorganized TAG configurationinformation.

FIG. 12 is a flowchart illustrating a method of reorganizing a TAG inaccordance with further yet another example of the present invention.

Steps S1500 to S1530 of FIG. 12 are the same as the steps S1400 to S1430of FIG. 11, and thus a detailed description thereof is omitted.

An eNB calculates a timing advance value regarding an added secondaryserving cell when receiving a random access preamble and sends an RARmessage indicative of the timing advance value to UE at step S1535.Here, the RAR message is a MAC message, and the timing advance value maybe indicated by a field within a MAC Random Access Response (RAR). Inthis case, the RAR message is mapped to a PDSCH indicated by a PDCCHthat is scrambled into a Random Access (RA)-Radio Network TemporaryIdentifier (RNTI) for identifying the UE in a random access procedureand is then transmitted. The PDCCH scrambled into the RA-RNTI istransmitted on a primary serving cell which provides a common searchspace.

In an embodiment, the RAR message may be indicated by a MAC ControlElement (CE). The field indicative of the timing advance value is calleda Timing Advance Command (TAC) field. In this case, the RAR message ismapped to a PDSCH indicated by a PDCCH scrambled into a Cell (C)-RNTIfor identifying the UE in a UE-specific space and then transmitted. ThePDCCH scrambled into the C-RNTI can be transmitted on a secondaryserving cell which provides a UE-specific search space.

In response to the RAR message, the UE checks the timing advance valueand performs TAG reorganization at step S1540. If a PDCCH scrambled intoan RA-RNTI is received, the UE checks a Random Access Preamble ID(RAPID) within the subheader of an RAR MAC PDU and checks a timingadvance value from a MAC RAR indicated by the subheader. If a PDCCHscrambled into a C-RNTI is received, the UE checks a TAC MAC CE extendedfrom the subheader of the MAC PDU or a value of an indicator (LCID)corresponding to the TAC MAC CE and checks a timing advance value fromthe MAC CE indicated by the subheader.

As an example of the TAG reorganization, if there is a TAG having thesame timing advance value as that of an existing TAG (a pTAG or ansTAG), the UE maps the added secondary serving cell to the correspondingTAG.

As another example of the TAG reorganization, if the timing advancevalue is different from a timing advance value applied to an existingTAG (a pTAG or an sTAG), the UE reorganizes the added secondary servingcell into a new TAG. Furthermore, a TAG ID having the smallest value,from among TAG IDs not used as a TAG ID in the UE, may be set as the TAGID of the new TAG, or a specific one of TAG IDs not used as a TAG ID inthe UE may be set as the TAG ID of the new TAG. For example, if a pTAG(TAG ID=0) and an sTAG (TAG ID=2) are configured in the UE, the TAG IDof the new TAG becomes 1. If a pTAG (TAG ID=0) and an sTAG (TAG ID=1)are configured in the UE, the TAG ID of the new TAG becomes 2.

FIGS. 10 to 12 illustrate embodiments in which an added secondaryserving cell is reorganized into an sTAG not a pTAG. If thereorganization of a TAG is not necessary because it is determined thatthe added secondary serving cell should be reorganized into the pTAGafter an eNB checks a timing advance value, however, there is a need fora method of the eNB informing UE of this process.

FIG. 13 is a flowchart illustrating a method of reorganizing a TAG inaccordance with further yet another example of the present invention.

Steps S1600 to S1625 of FIG. 13 are the same as the steps S1500 to S1525of FIG. 12, and thus a detailed description thereof is omitted.

An eNB can obtain a timing advance value regarding an added secondaryserving cell through a random access procedure. If it is correct thatthe added secondary serving cell is mapped to a pTAG based on the timingadvance value, the eNB determines to not perform TAG reorganization atstep S1630.

Next, the eNB sends a PDCCH order to UE at step S1635. Here, the PDCCHorder may mean that a current TAG reorganization has been determined. Inan embodiment, the PDCCH order may mean the stop of an ongoing randomaccess procedure.

If the PDCCH order for the secondary serving cell is received during arandom access procedure on an added secondary serving cell within apTAG, UE stops the ongoing random access procedure at step S1640. Here,the ongoing random access procedure is stopped only when parameterswithin a PDCCH order recognized as the stop of a random access procedureare the same as parameters within a PDCCH order received by the addedsecondary serving cell for the ongoing random access procedure.

FIG. 14 is a flowchart illustrating a method of UE reorganizing a TAG inaccordance with an example of the present invention.

Referring to FIG. 14, UE receives secondary serving cell configurationinformation or the secondary serving cell configuration information andreorganized TAG configuration information from an eNB at step S1700. Thesecondary serving cell configuration information and the TAGconfiguration information may be received through one RRC connectionreconfiguration procedure or different RRC connection reconfigurationprocedures. In an embodiment, the TAG configuration information may beincluded in the secondary serving to cell configuration information.

The UE checks whether the secondary serving cell configurationinformation is for adding or releasing a secondary serving cell at stepS1705. If the secondary serving cell configuration information includesa field ‘sCellToReleaseList’, the secondary serving cell configurationinformation is for releasing the secondary serving cell. In contrast, ifthe secondary serving cell configuration information includes a field‘sCellToAddModList’, the secondary serving cell configurationinformation is for adding the secondary serving cell.

If the secondary serving cell configuration information is for releasingthe secondary serving cell, the UE releases the configuration of thesecondary serving cell at step S1710. For example, if the UE receivesthe secondary serving cell configuration information and the reorganizedTAG configuration information through one RRC connection reconfigurationprocedure, the UE releases the secondary serving cell. For anotherexample, if the UE receives the secondary serving cell configurationinformation and the reorganized TAG configuration information throughdifferent RRC connection reconfiguration procedures, the UE releases thesecondary serving cell and reorganizes a TAG.

If, as a result of the check, the secondary serving cell configurationinformation is for adding the secondary serving cell, the UE checkswhether TAG configuration information has been received or not at stepS1715. If the UE has not received the TAG configuration information, itmay mean that an eNB has not sent the TAG configuration information orthat the TAG configuration information is not included in the secondaryserving cell configuration information. As described in Paragraph(2-2-2), it may mean that i) a TAG ID=0, ii) a TAG ID=‘Null’, or iii)TAG configuration information is not included in the secondary servingcell configuration information.

If, as a result of the check at the step S1715, the UE has not receivedthe TAG configuration information, the UE reorganizes the addedsecondary serving cell into a pTAG by default, assigns the addedsecondary serving cell to a new sTAG, or does not assign any TAG ID tothe added secondary serving cell at step S1720.

The UE receives a PDCCH order from the eNB at step S1725. In responsethereto, the UE sends a random access preamble to the eNB at step S1730.

The UE receives a reorganization-complete message from the eNB at stepS1735 and reorganizes the TAG in response to the reorganization-completemessage at step S1740. The reorganization-complete message may be, forexample, at least of an RAR message including a timing advance value, anRRC connection reconfiguration message, and a PDCCH order.

For example, if the reorganization-complete message is the RAR message,the reorganization-complete message may be a MAC RAR or a MAC CE. If aPDCCH scrambled into an RA-RNTI is received, the UE can check a MAC RARincluding a timing advance value from a PDSCH indicated by the PDCCH. Ifa PDCCH scrambled into a C-RNTI is received, the UE can check a MAC CEincluding a timing advance value from a PDSCH indicated by the PDCCH.Next, the UE performs TAG reorganization. As an example of the TAGreorganization, if the timing advance value has the same timing advancevalue applied to an existing TAG (a pTAG or an sTAG), the UE maps theadded secondary serving cell to a corresponding TAG. As another exampleof the TAG reorganization, if the timing advance value is different froma timing advance value applied within an existing TAG (a pTAG or ansTAG) and the number of TAGs now configured in the UE is smaller than amaximum number of TAGs that can be configured, the UE designates atemporary TAG ID as the TAG ID of a new sTAG and maps the addedsecondary serving cell to the TAG. As yet another example of the TAGreorganization, if the timing advance value is different from a timingadvance value applied within an existing TAG (a pTAG or an sTAG) and thenumber of TAGs now configured in the UE is the same as a maximum numberof TAGs that can be configured, the UE performs one of the followingoperation. That is, i) the UE may determine that the timing advancevalue for the added secondary serving cell is not valid and disregardthe received timing advance value. ii) The UE may deactivate the addedsecondary serving cell in order to prevent uplink transmission within acorresponding TAG. This is because there may be a problem in uplinktransmission within the TAG because a new TAG ID and the configurationof a current TAG are not valid. iii) The UE may release theconfiguration of the added secondary serving cell instead of thedeactivation operation.

For another example, if the reorganization-complete message is the RRCconnection reconfiguration message, the reorganization-complete messageincludes reorganized TAG configuration information. The reorganized TAGconfiguration information indicates a specific TAG ID in addition to apTAG. In this case, the UE reorganizes the added secondary serving cellinto a TAG having the specific TAG ID.

For yet another example, if the reorganization-complete message is thePDCCH order, the reorganization-complete message is an indicator havinga meaning that a random access procedure in the added secondary servingcell is stopped. In this case, the UE maintains the added secondaryserving cell in a temporally mapped TAG (e.g., a pTAG) and does notreorganize the TAG.

If, as a result of the check at the step S1715, the UE has received theTAG configuration information, the UE checks whether a TAG ID indicatedby the TAG configuration information is a temporary TAG ID or a normalTAG ID and configures a temporary TAG or a new sTAG in response to theTAG ID indicated by the TAG configuration information at step S1745.Next, the UE performs the step S1725 to the step S1740.

FIG. 15 is a flowchart illustrating a method of an eNB reorganizing aTAG in accordance with an example of the present invention.

Referring to FIG. 15, an eNB determines to add or release a secondaryserving cell at step S1800. For example, if a frequency band necessaryfor UE is reduced or access to a secondary serving cell of a serving eNBis released due to a handover, the eNB can determine to release asecondary serving cell configured in UE. For another example, if abandwidth supported for UE is increased or the new cell of a target eNBis accessed due to a handover, the eNB can determine to additionallyconfigure a secondary serving cell in UE. The addition or release of thesecondary serving cell corresponds to the change or update of secondaryserving cell configuration information.

If a change of secondary serving cell configuration informationcorresponds to the release of the secondary serving cell at step S1805,the eNB sends an RRC connection reconfiguration message for releasingthe secondary serving cell to the UE at step S1810.

In contrast, if a change of secondary serving cell configurationinformation corresponds to the addition of the secondary serving cell atstep S1805, the eNB checks whether a timing advance value for the addedsecondary serving cell can be obtained at step S1815. If the eNB hasobtained the timing advance value for the added secondary serving cellor can obtain the timing advance value for the added secondary servingcell, the eNB reorganizes the added secondary serving cell into aspecific TAG at step S1820 and sends TAG configuration information,indicating a TAG ID to be mapped to the added secondary serving cell, tothe UE at step S1825. Here, the TAG configuration information may beincluded in secondary serving cell configuration information andtransmitted or may be transmitted separately from secondary serving cellconfiguration information. In contrast, if a serving cell having aspecific frequency band is always provided through an FSR or a remoteradio head, the eNB cannot secure a timing advance value because theserving cell having the specific frequency band and a serving celldirectly served by the eNB have different timing advance values andbelong to different TAGs in relation to all pieces of UE within theservice coverage of the eNB.

If, as a result of the check at step S1815, a timing advance value forthe added secondary serving cell cannot be obtained, the eNB maps theadded secondary serving cell to a temporary TAG ID or sets a TAG IDregarding the added secondary serving cell to ‘Null’ or does notgenerate TAG configuration information. Next, the eNB sends thesecondary serving cell configuration information for adding thesecondary serving cell or the secondary serving cell configurationinformation and TAG configuration information to the UE at step S1830.The secondary serving cell configuration information and the TAGconfiguration information may be transmitted through one RRC connectionreconfiguration procedure or different RRC connection reconfigurationprocedures. In an embodiment, the TAG configuration information may beincluded in the secondary serving cell configuration information. If aTAG regarding the secondary serving cell is set to ‘Null’ or a TAG ID=0,it may be considered that the added secondary serving cell is temporallymapped to a pTAG or that the added secondary serving cell is not mappedto any TAG.

The eNB sends a PDCCH order to the UE at step S1835. In responsethereto, the eNB receives a random access preamble from the UE on theadded secondary serving cell at step S1840.

The eNB obtains a timing advance value for the added secondary servingcell when receiving the random access preamble and reorganizes the addedsecondary serving cell into a specific TAG based on the timing advancevalue at step S1845. For example, if the timing advance value is thesame as that of a pTAG in the state in which the added secondary servingcell has been reorganized into the pTAG when adding the secondaryserving cell, the eNB does not reorganize the TAG. For another example,if the timing advance value is different from that of a pTAG, but is thesame as that of another sTAG in the state in which the added secondaryserving cell has been reorganized into the pTAG when adding thesecondary serving cell, the eNB reorganizes the added secondary servingcell into the sTAG. For yet another example, if the timing advance valueis different from that of a pTAG and also different from that of anothersTAG in the state in which the added secondary serving cell has beenreorganized into the pTAG when adding the secondary serving cell, theeNB reorganizes the added secondary serving cell into a new sTAG.

The eNB sends a reorganization-complete message for informing the UE ofthe reorganized TAG to at step S1850. The reorganization-completemessage can be at least one of, for example, an RAR message including atiming advance value, an RRC connection reconfiguration message, and aPDCCH order.

For example, if the reorganization-complete message is the RAR message,the reorganization-complete message may be a MAC RAR or a MAC CE. If aPDCCH scrambled into an RA-RNTI is received, the UE can check a MAC RARincluding a timing advance value from a PDSCH indicated by the PDCCH. Ifa PDCCH scrambled into a C-RNTI is received, the UE can check a MAC CEincluding a timing advance value from a PDSCH indicated by the PDCCH. Inthis case, the UE implicitly reorganizes the added secondary servingcell into any one existing TAG based on the timing advance value.

For another example, if the reorganization-complete message is the RRCconnection reconfiguration message, the reorganization-complete messageincludes reorganized TAG configuration information. The reorganized TAGconfiguration information indicates a specific TAG ID in addition to apTAG. In this case, the UE reorganizes the added secondary serving cellinto a TAG having the specific TAG ID.

For yet another example, if the reorganization-complete message is thePDCCH order, the reorganization-complete message is an indicator havinga meaning that a random access procedure in the added secondary servingcell is stopped. In this case, the UE maintains the added secondaryserving cell in a temporally mapped TAG (e.g., a pTAG) and does notreorganize the TAG.

FIG. 16 is a block diagram showing UE and an eNB for sending signalsregarding uplink synchronization in accordance with an example of thepresent invention.

Referring to FIG. 16, the UE 1900 includes a reception unit 1905, a UEprocessor 1910, and a transmission unit 1920. The UE processor 1910includes an RRC processing unit 1911 and a random access processing unit1912.

The reception unit 1905 receives secondary serving cell configurationinformation, TAG configuration information, a PDCCH order, an RARmessage, and a reorganization-complete message from an eNB 1950. Thereorganization-complete message can be at least one of, for example, anRAR message including a timing advance value, an RRC connectionreconfiguration message, and a PDCCH order.

The RRC processing unit 1911 generates a message used in an RRCprocedure or receives the message from the eNB 1950. The RRC procedurecan include, for example, an RRC connection establishment procedure andan RRC connection reconfiguration procedure. A message used in the RRCconnection reconfiguration procedure can include at least one ofsecondary serving cell configuration information and TAG configurationinformation.

The RRC processing unit 1911 configures a primary serving cell and atleast one secondary serving cell, used in a CA, in the UE 1900 in theform of the CA. A procedure for additionally configuring a secondaryserving cell in the UE 1900 or releasing a secondary serving cellconfigured in the UE 1900 can be indicated by secondary serving cellconfiguration information.

Meanwhile, the RRC processing unit 1911 reorganizes a TAG based on atleast one of secondary serving cell configuration information and a TAGID indicated by TAG configuration information. The RRC processing unit1911 reorganizes the TAG so that the secondary serving cell is includedin the TAG. For example, if the secondary serving cell configurationinformation includes an information field for adding or releasing aspecific secondary serving cell, the RRC processing unit 1911 adds orreleases the specific secondary serving cell based on an order of theinformation field and updates or reorganizes a TAG to or from which thespecific secondary serving cell is added or released.

Furthermore, if the TAG configuration information indicates that aspecific secondary serving cell is mapped to a TAG having a specific ID,the RRC processing unit 1911 reorganizes the specific secondary servingcell into the TAG having the specific ID based on the TAG configurationinformation. If the specific TAG ID=0 or the TAG ID=‘Null’, the RRCprocessing unit 1911 determines that the specific secondary serving cellbelongs to a pTAG by default and reorganizes the specific secondaryserving cell into the pTAG. In an embodiment, the RRC processing unit1911 does not reorganize the specific secondary serving cell into anyTAG. If a TAG has a temporary value, that is, a specific TAG ID≠0, theRRC processing unit 1911 reorganizes the specific secondary serving cellinto a temporary TAG ID.

Furthermore, the RRC processing unit 1911 can reorganize the TAG basedon the timing advance value regarding the secondary serving cellreceived from the random access processing unit 1912. As an example ofthe TAG reorganization, if there is a TAG having the same timing advancevalue as that of an existing TAG (a pTAG or an sTAG), the RRC processingunit 1911 maps the added secondary serving cell to the correspondingTAG. As another example of the TAG reorganization, if the timing advancevalue is different from a timing advance value applied within anexisting TAG (a pTAG or an sTAG) and the number of TAGs now configuredin the UE 1900 is smaller than a maximum number of TAGs that can beconfigured, the RRC processing unit 1911 designates a temporary TAG IDas the TAG ID of a new sTAG and maps the added secondary serving cell tothe TAG. As yet another example of the TAG reorganization, if the timingadvance value is different from a timing advance value applied within anexisting TAG (a pTAG or an sTAG) and the number of TAGs now configuredin the UE 1900 is the same as a maximum number of TAGs that can beconfigured, the RRC processing unit 1911 performs one of the followingoperations. That is, i) the RRC processing unit 1911 determines that thetiming advance value for the added secondary serving cell is not validand disregards the received timing advance value. ii) The RRC processingunit 1911 deactivates the added secondary serving cell in order toprevent uplink transmission within a corresponding TAG. This is becausethere may be a problem in uplink transmission within a TAG because a newTAG ID and the configuration of a current TAG are not valid. iii) TheRRC processing unit 1911 may release the added secondary serving cellinstead of the deactivation operation.

The random access processing unit 1912 generates a random accesspreamble in response to a PDCCH order and sends the random accesspreamble to the transmission unit 1920. Furthermore, the random accessprocessing unit 1912 obtains a timing advance value regarding asecondary serving cell from a Random Access Response (RAR) messagereceived from the reception unit 1905 and controls uplinksynchronization regarding the secondary serving cell based on the timingadvance value. Furthermore, the random access processing unit 1912 canprovide the timing advance value to the RRC processing unit 1911 so thatthe RRC processing unit 1911 reorganizes a TAG.

The transmission unit 1920 sends the random access preamble or an RRCmessage to the eNB 1950.

The eNB 1950 includes a transmission unit 1955, a reception unit 1960,and an eNB processor 1970. The eNB processor 1970 includes an RRCprocessing unit 1971 and a random access processing unit 1972.

The transmission unit 1955 sends secondary serving cell configurationinformation, TAG configuration information, a PDCCH order, and an RAR tothe UE 1900. Here, the transmission unit 1955 may send the secondaryserving cell configuration information including the TAG configurationinformation or may send the TAG configuration information separatelyfrom the secondary serving cell configuration information.

The reception unit 1960 receives a random access preamble and an RRCmessage from the UE 1900.

The RRC processing unit 1971 determines to add or release a secondaryserving cell for the UE 1900. For example, if a frequency band necessaryfor the UE 1900 is reduced or access to the secondary serving cell of aserving eNB is released due to a handover, the RRC processing unit 1971can determine to release a secondary serving cell configured in the UE1900. For another example, if a bandwidth supported for the UE 1900 isincreased or the new cell of a target eNB is accessed due to a handover,the RRC processing unit 1971 can determine to additionally configure asecondary serving cell in the UE 1900. The addition or release of thesecondary serving cell corresponds to the change or update of secondaryserving cell configuration information.

If a change of the secondary serving cell configuration informationcorresponds to the release of the secondary serving cell, the RRCprocessing unit 1971 generates an RRC connection reconfiguration messagefor releasing the secondary serving cell and sends the RRC connectionreconfiguration message to the transmission unit 1955.

In contrast, if a change of the secondary serving cell configurationinformation corresponds to the addition of the secondary serving cell,the RRC processing unit 1971 checks whether the timing advance value ofthe secondary serving cell can be obtained. If, as a result of thecheck, the RRC processing unit 1971 has secured the timing advance valueof the secondary serving cell or can secure the timing advance value ofthe secondary serving cell, the RRC processing unit 1971 reorganizes thesecondary serving cell into a specific TAG, generates TAG configurationinformation indicative of a TAG ID to which the secondary serving cellwill be mapped, sends the TAG configuration information to thetransmission unit 1955. Here, the TAG configuration information may beincluded in secondary serving cell configuration information or may begenerated separately from secondary serving cell configurationinformation.

If, as a result of the check, the RRC processing unit 1971 is unable tosecure the timing advance value of the secondary serving cell, the RRCprocessing unit 1971 maps the secondary serving cell to a temporary TAGID, sets a TAG ID regarding the added secondary serving cell to ‘Null’,or does not generate TAG configuration information. Furthermore, the RRCprocessing unit 1971 generates secondary serving cell configurationinformation for adding the secondary serving cell or the secondaryserving cell configuration information and TAG configuration informationand sends the secondary serving cell configuration information foradding the secondary serving cell or the secondary serving cellconfiguration information and the TAG configuration information to thetransmission unit 1955.

The RRC processing unit 1971 may include the secondary serving cellconfiguration information and the TAG configuration information in oneRRC connection reconfiguration message or in different RRC connectionreconfiguration messages. In an embodiment, the RRC processing unit 1971may include the TAG configuration information in the secondary servingcell configuration information. If a TAG ID regarding the secondaryserving cell is ‘Null’ or the TAG ID=0, it may be considered that theadded secondary serving cell is temporally mapped to a pTAG or that theadded secondary serving cell is not mapped to any TAG.

The random access processing unit 1972 generates a PDCCH order in orderto obtain a timing advance value for the uplink synchronization of theadded secondary serving cell and sends the PDCCH order to thetransmission unit 1955. As a response thereto, the reception unit 1960receives a random access preamble from the UE 1900 on the secondaryserving cell.

The random access processing unit 1972 obtains a timing advance valuefor the added secondary serving cell when receiving the random accesspreamble, and the RRC processing unit 1971 reorganizes the addedsecondary serving cell into a specific TAG based on the timing advancevalue. For example, if the timing advance value is the same as that of apTAG in the state in which an added secondary serving cell has beenreorganize into the pTAG when adding the secondary serving cell, the RRCprocessing unit 1971 does not reorganize a TAG. For another example, ifthe timing advance value is different from that of a pTAG and is thesame as another sTAG in the state in which an added secondary servingcell has been reorganize into the pTAG when adding the secondary servingcell, the RRC processing unit 1971 reorganizes the added secondaryserving cell into the sTAG. For yet another example, if the timingadvance value is different from that of a pTAG and is different anothersTAG in the state in which an added secondary serving cell has beenreorganize into the pTAG when adding the secondary serving cell, the RRCprocessing unit 1971 reorganizes the added secondary serving cell into anew sTAG.

The RRC processing unit 1971 or the random access processing unit 1972generates a reorganization-complete message for informing the UE 1900 ofthe reorganized TAG and sends the reorganization-complete message to thetransmission unit 1955. The reorganization-complete message can be atleast one of, for example, an RAR message including a timing advancevalue, an RRC connection reconfiguration message, and a PDCCH order.

For example, if the reorganization-complete message is the RAR message,the reorganization-complete message can be a MAC RAR or a MAC CE. If aPDCCH scrambled into an RA-RNTI is received, the random accessprocessing unit 1972 can check a MAC RAR including a timing advancevalue from a PDSCH indicated by a PDCCH. If a PDCCH scrambled into aC-RNTI is received, the random access processing unit 1972 can check aMAC CE including a timing advance value from a PDSCH indicated by aPDCCH. In this case, the RRC processing unit 1971 implicitly reorganizesthe added secondary serving cell into any one existing TAG based on thetiming advance value.

For another example, if the reorganization-complete message is the RRCconnection reconfiguration message, the reorganization-complete messageincludes reorganized TAG configuration information. The reorganized TAGconfiguration information indicates a specific TAG ID other than a pTAG.In this case, the RRC processing unit 1971 reorganizes the addedsecondary serving cell into a TAG having the specific TAG ID.

For yet another example, if the reorganization-complete message is thePDCCH order, the reorganization-complete message is an indicator havinga meaning that a random access procedure in the added secondary servingcell is stopped. In this case, the RRC processing unit 1971 maintainsthe added secondary serving cell in a a temporally mapped TAG (e.g., apTAG) and does not reorganize a corresponding TAG.

In accordance with the present invention, a procedure can be simplifiedand TAG reorganization can be performed more rapidly because TAGconfiguration information for reorganizing a TAG does not need to beseparately transmitted. Furthermore, an eNB may explicitly order TAGreorganization for UE or UE can implicitly perform TAG reorganization.

While some exemplary embodiments of the present invention have beendescribed with reference to the accompanying drawings, those skilled inthe art may change and modify the present invention in various wayswithout departing from the essential characteristic of the presentinvention. Accordingly, the disclosed embodiments should not beconstrued as limiting the technical spirit of the present invention, butshould be construed as illustrating the technical spirit of the presentinvention. The scope of the technical spirit of the present invention isnot restricted by the embodiments, and the scope of the presentinvention should be interpreted based on the following appended claims.Accordingly, the present invention should be construed as covering allmodifications or variations derived from the meaning and scope of theappended claims and their equivalents.

What is claimed is:
 1. A user equipment (UE) comprising: a receiver toreceive a first field comprising a first serving cell index (SCellindex)to release a serving cell (SCell) associated with the first SCellindexand a second field comprising at least one SCellIndex to add one or moreSCell associated with the at least one SCellIndex and an identifier of atiming advance group (TAG) associated with the one or more SCell; aradio resource control (RRC) processor to release the SCell associatedwith the first SCellIndex and to add the one or more SCell as anavailable SCell for use with the UE and to associate the one or moreSCell with another available SCell associated with same TAG identifier.2. A method of user equipment (UE), comprising: receiving a first fieldcomprising a first serving cell index (SCellindex) to release a servingcell (SCell) associated with the first SCellindex; receiving a secondfield comprising at least one SCellindex to add one or more SCellassociated with the at least one SCellindex and an identifier of atiming advance group (TAG) associated with the one or more SCell;releasing the SCell associated with the first SCellindex for use withthe UE; adding the one or more SCell as available SCell for use with theUE; and associating the one or more SCell with another available SCellassociated with same TAG identifier.